The present invention relates to blood pumps usable as implantable ventricular assist devices, and more particularly to an improved blood pump device with an integrated ultrasonic flow sensor.
In certain disease states, the heart lacks sufficient pumping capacity to maintain adequate blood flow to the body's organs and tissues. For example, conditions such as ischaemic heart disease and hypertension may leave the heart unable to fill and pump efficiently. This condition, also called congestive heart failure, may lead to serious health complications, including respiratory distress, cardiac asthma, and even death. In fact, congestive heart failure is one of the major causes of death in the Western world.
This inadequacy of the heart can be alleviated by providing a mechanical pump also referred to as a ventricular assist device (“VAD”) to supplement the pumping action of the heart. VADs may be used to assist the right ventricle, the left ventricle, or both. For example, a VAD may assist the left ventricle by mechanically pumping oxygenated blood from the left ventricle into the aorta. In this case, the pump is implanted within the body of the patient, an inflow conduit is attached to the left ventricle, and an outflow conduit is attached to the aorta. For example, where the pump is implanted below the heart or at the bottom of the heart, the outflow conduit may be a flexible conduit extending generally upwardly, from the outlet of the pump to the aorta. The pump receives blood from the left ventricle and then pushes it into the aorta for distribution throughout the body. This reduces the strain on the heart by reducing the volume of blood that the heart is responsible for moving.
U.S. Pat. Nos. 7,575,423, 7,976,271, 8,007,254, and 8,419,609, the disclosures of which are hereby incorporated by reference, disclose certain rotary blood pumps which can be used as ventricular assist devices. These pumps are electrically powered. Typically, these and other electrically powered implantable pumps are connected through a cable, commonly referred to as a “driveline”, to a control device which supplies electric power to the pump and controls its operation. The control device may be external to the patient's body, in which case the driveline extends through the skin. It has also been proposed to use implanted control devices which receive power from an external source by means of an implanted induction coil.
It is desirable to monitor certain parameters of the pump, including for instance the rate of blood flow through the VAD. Flow information can be used to detect abnormal operating conditions, such as blockage of the outflow conduit or a “suction” condition, where the left ventricle is not refilled fast enough to keep the pump supplied with blood, and also can be used to provide feedback control of the pump. However, blood flow through a VAD is difficult to monitor because it often cannot be measured directly. It would not be desirable to install a bulky sensor in the path of the flowing blood, as the sensor could obstruct the blood flow and reduce the effectiveness of the pump.
One solution that has been proposed is to measure blood flow indirectly. This can be achieved by measuring blood pressure at both the inflow and outflow sections of the pump, and then mathematically computing blood flow. Pressure sensors have been incorporated into VADs for the purpose of monitoring blood flow through the VAD. Blood flow also can be determined indirectly from operational parameters of the pump as, for example, the speed of the pump and the power used by the pump.
Other solutions have been proposed that involve measuring blood flow through the pump directly. This can be achieved, for instance, through the use of an ultrasonic flow probe. For example, it has been proposed to provide an ultrasonic flow probe around mounted on the outflow cannula. Similarly, European Patent EP1046403 discloses a blood circulation device with ultrasonic flow sensors attached to the inflow cannula or “blood feeding pipe.” In these proposed solutions, blood flow can be monitored directly for enhanced control over the therapeutic qualities of the pump. However, these solutions require an additional structure to hold the ultrasonic flow probe. Moreover, as further discussed below, certain types of ultrasonic flow measurement can be used only in a rigid conduit. Where the flow is measured along a flexible conduit, the additional structure typically must have appreciable bulk to hold a portion of the flexible conduit in a fixed configuration. Also, these arrangements require an additional cable extending to the additional structure housing the flow probe. These factors make it more difficult to implant the system in the body.
Thus, despite very considerable effort devoted in the art to development of ventricular assist devices, further improvement would be desirable. Particularly, there is a need for a VAD which can provide the benefits of direct flow measurement without substantially increasing the difficulty of implanting the device.